Thin film transistor array panel is used as a circuit substrate to individually drive each pixel, such as of liquid crystal display or organic electro luminescence display. The thin film transistor array panel includes a plurality of pixels arranged in a matrix and a plurality of signal lines for driving the pixels such as gate lines for transmitting scanning signals and data lines for transmitting data signals. Each pixel includes a pixel electrode, and a thin film transistor (TFT) connected to the gate lines and the data lines for controlling the data signals.
At this time, signal lines such as gate lines and the data lines includes metal materials, and the pixel electrodes are usually made of transparent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO). ITO or IZO in a liquid crystal display may be used as a contact assistant layer to reinforce contact characteristics when connecting the gate lines and the date lines to external drive circuits.
In order to prevent delay or distortion of signals, the signal lines are generally made of materials having low resistivity such as aluminum or aluminum alloy. However, since the physical and the chemical properties of the aluminum or aluminum alloy is not good, that is, the aluminum or aluminum alloy is easily oxidized and broken, when connecting other conductive material in a contact portions, accordingly the characteristics of semiconductor devices are deteriorated. Furthermore, in the case that ITO and IZO as a transparent electrode such as in a liquid crystal display is used to reinforce contact portions of aluminum. However, because of the poor contact properties between aluminum or aluminum alloy and ITO, or IZO, a different material such as Ti, Cr, Mo is then inserted therebetween. Accordingly, the manufacturing method is complicated and production costs are increased.
Furthermore, when removing aluminum in the contact portions to expose a material layer having good contact characteristic, an under-cut structures are frequently generated by over-etching the Al containing metal under a sidewall of the contact portions. The undercut yields disconnection or poor profile of the subsequently-formed layer near the undercut to increase the contact resistance of the contact portions.